The present invention relates to a disc drive motor for rotary drive of a disk used as an information signal recording medium.
In an inner hub type disk drive motor, the hub which loads a disk at its circumference itself forms a rotor of the motor. Therefore, the hub must, in addition to functioning as the disk loading body, also function as the yoke which together with the rotor case of the motor form a magnetic circuit. In addition, the hub must be plated or provided with other rust preventive measures in order to eliminate adhesion of dust by rust at the disc surface. Moreover, a magnetic disc is required to reduce, as much as possible, the leakage of magnetic flux from the hub toward the magnetic disc surface.
FIG. 5 indicates structure of a hub used for a conventional disc drive motor. In FIG. 5, a hub 2 is made through forging or casting from aluminum, aluminum alloy or the like. A yoke 3 made of soft magnetic material is thermocompression bonded or adhered to the hub 2.
In the conventional art explained above, the hub as a whole is formed almost cylindrically with a flange. The external circumference of the hub is to be engaged with the clamp member holding the disc and the clamp member is to be deposited and positioned on the flange. Therefore, the external circumference of the hub and the flange surface are required to be finished with high accuracy.
Furthermore, in the above-described conventional art, the hub and the yoke are formed separately, and the yoke is adhered or thermocompression bonded to the hub so that the hub and the yoke are united into one body. Therefore, the fixing strength of the yoke to the hub is low and unstable, and the yoke is liable to be rotated with respect to the hub. Furthermore, in order to fix a disc on the flange with a clamp mechanism, the flange of the hub is required to have a considerably large bending strength. However, in the conventional art, since the yoke is not extended to the flange portion of the hub, the bending strength of the flange of the hub is insufficient. Even if the yoke is fixed to also the flange portion of the hub as well, the bending strength of the flange of the hub is still insufficient.
On the other hand, if the hub is made of stainless steel or iron material, the rigidity of the hub becomes large. However, the force of inertia also becomes large, so that a long time is required for starting and stopping, resulting in a particular problem at the time for stoppage.